The use of lasers to pattern materials by removing material is known. Typically, such a process may compete with a conventional photolithographic method. Some observations may be made to compare laser patterning and photolithography.
Photolithography is much more widespread for many applications than laser ablation; yet, it entails many more processing steps. First the material to be patterned is covered with a layer of material, termed photoresist. The photoresist is exposed with a light pattern. Then, it is developed, leaving a patterned photoresist. The resist then serves as a mask for an etching step. The use of wet etch (acid or alkaline) or plasma etch (RIE, ion milling, or plasma) are some of the methods that will remove the exposed material at a much higher rate than the resist. Once the underlying material has been suitably etched, the cycle is completed by removing the resist and cleaning the patterned layer. It is only then that the permanently desired features can be quantitatively evaluated.
By contrast, etching by laser can be a single step process in which a high intensity pulsed light source that forms a pattern can directly etch the material away. There are other variations where, for example, the laser may be used to ablatively pattern an etch block and the subsequent material etch is performed conventionally. In both cases, the laser etch method can be used to reduce the number of process steps by a factor of about 3 to 10. This translates to enormous economic impact for the manufacturing of many types of electronic and other classes of elements. Typical electronic elements which can be ablated by laser include semiconductor chips, flat panel displays, interconnect structures, and multichip modules.
To date, one drawback of direct laser ablation has been the controllability of the ablating laser process. Forming the light pattern to give precisely the correct etching characteristics and pattern definition is one difficulty to overcome. The materials response as related to wall slope and feature dimension.
In co-pending applications for "Apparatus and Process for the Production of Fine Line Metal Traces" (Ser. No. 08/058,906, filed May 6, 1993, now U.S. Pat. No. 5,364,493) "Use of Fresnel Zone Plates for Material Processing" (Ser. No. 07/940 008, filed Sep. 3, 1992, now U.S. Pat. No. 5,362,940), "Apparatus and Process for Nozzle Production Utilizing Computer Generated Holograms" (Ser. No. 08/177,108, filed Jan. 3, 1994), "Apparatus and Process for optically Ablated Openings Having Designed Profile" (Ser. No 08/215,851 filed Mar. 21 1994) and "Direct Etch Process for the Manufacture of High Density Multichip Modules" (Ser. No 08/231,704, filed Apr. 29, 1994), the inventors disclose both the use of phase masks and ablative methods of forming suitable features for various applications. These applications are incorporated herein by reference.